The kinetics of the de-and remineralization reactions involved in the caries process at enamel and dentin surfaces will be investigated at constant concentration, using the dual Constant Composition (DCC) method. Under-and supersaturations will be maintained using multiple ion specific electrodes to control the addition of titrants. Studies will include etched and softened surfaces (enamel and dentin) and subsurface lesions (enamel). Solid phases will be investigated by scanning electron and field emission microscopy, X-ray microradiography, micro-hardness tests, polarized light microscopy, EDX, ESCA, and SIMS. The reactions will be studied both in the presence and absence of carbon dioxide of known partial pressures and in the presence of other ions such as zinc, magnesium, silicon, copper, cadmium, aluminum, iron, fluoride, phosphoditrate and polypeptides. A flow-through Constant Composition (CC) method will be used to study the mechanism of nucleation and growth of calcium phosphate phases at tooth surfaces and on immobilized and Langmuir Blodgett films of macromolecules. It will be possible to treat the mineralizing surfaces, using a second flow-through loop with various reagents simulating processes that take place during tooth brushing with dentifrices. CC and DCC methods will be used to investigate the kinetics of transformation of calcium phosphate phases ranging from amorphous calcium phosphate to hydroxyapatite. Aggregation and electrophoretic mobility measurements of dentin, calculus, enamel, and synthetic calcium phosphates will be determined in the presence of both simple inorganic ions and separated salivary proteins.